C'mon, Let's Twist Again, Like We Did (This) Summer

Dirk Trauner: natural products chemist, vision researcher, neuropharmacologist,
. . . carbon nano-tube enthusiast?

Apparently, it's "crazy saturated hydrocarbons" month here at JLC. An astute observer clued me in to the Trauner group's latest pursuit - polytwistane. Studied for five decades by organic chemistry pioneers such as Whitlock, Deslongchamps, Oka, and von Rague Schleyer, twistanes have been tricky to coax into existence, owing to their propensity to rearrange into more stable adamantane.

In a 'gedanken' (thought) experiment, Allen, Schreiner, and Trauner mentally "add" bridging ethane units to twistane, stretching it out into a pseudo-helical oligomer (Chem. Eur. J.):

Chem. Eur. J. 2014, 1638.

Some fascinating molecular motifs fall out of their modeling studies. For example, unlike adamantane, polytwistane has three distinctly different C-C bond lengths, a factor chalked up to strain energy. However, it's in no danger of falling apart - the researchers calculate a "very modest" strain energy (~1.6 kcal / mol CH). All the hydrogens occupy positions on the outside (convex) surface of the tube. Finally, note that polytwistane is formally a polymerized version of acetylene, which we'll come back to later.

Emboldened by these in silico  results, Trauner and team take to synthesizing a basic unit of polytwistane, so-called "tritwistane" (Org. Biomol. Chem.). Starting from laticyclic polyenes -- think bicyclo[2.2.2]octene, connected end-to-end -- the researchers try a variety of electrophilic conditions to form the bond in question. Eventually, a combination of bromination / radical reduction produces the simple tritwistane oligomer:

Org. Biomol. Chem., 2014, 108.

At the close of this paper, Trauner deadpans that "attempts to synthesize polytwistane . . .from acetylene itself are ongoing in our laboratory..." Sounds like a tough nut to crack, but if he succeeds, he and his collaborators will have access to a rather rigid, narrow, twisted new material certain to possess interesting properties.

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